Immunoglobulins are a group of structurally related proteins composed of heavy and light chains comprised of variable and constant domains. The variable regions of the heavy and light chains determine the molecular specificity of the complete molecule. Immunoglobulins are categorized as IgG, IgM, IgE, IgD, or IgA based on the identity of the constant regions of their heavy chains Immunoglobulin A (IgA) comprises an alpha (a) constant region in its heavy chains.
IgA is produced by plasma cells located along the mucosal linings of the respiratory, gastrointestinal, and genitourinary tracts. IgA molecules bind to invading pathogens and weaken their ability to penetrate the mucosal layer and to enter the inner tissue and blood stream of the host. See generally J. G. Nedrud et al., “Adjuvants and the Mucosal Immune System”, Topics in Vaccine Adjuvant Research, (Spiggs, D. E., Koff, W. C., Eds.) CRC Press, Boca Raton, Fla. (1990). IgA binds to receptors on the cell surface of phagocytic leukocytes and thereby facilitates antibody-dependent cell-mediated killing of invading pathogens. IgA can also bind allergenic substances, thereby preventing the allergens from binding IgE or activating T cells responsible for delayed-type hypersensitivity.
A deficiency of IgA can occur transiently, for example upon exposure to certain drugs or in response to various infections, or permanently, as in patients with congenital IgA deficiency.
It has been found that individuals with low IgA production are more prone to various inflammatory diseases, such as autoimmune diseases and allergies, than those with normal IgA levels. Thus, increasing the levels of either total IgA or antigen-specific IgA may treat or prevent inflammatory diseases.